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In this paper, a homogenized multiphase lattice Boltzmann (LB) model is established for parallelly simulating immiscible two-phase flow in both solid-free regions (pore scale) and porous areas (continuum scale). It combines the color-gradient multiphase model with the Darcy–Brinkman–Stokes method by adding a term that includes surface force and drag force of porous matrix to multiple-relaxation-time LB equation in moment space. Moreover, an improved algorithm is proposed to characterize and implement the apparent wettability in the locally homogenized porosity field. Validations and test cases are given to demonstrate the accuracy and robustness of this new model, as well as its applicability for trans-scale fluid simulation of transport and sorption behavior from porous (Darcy flow) area to free (Stokes flow) area. For practicality, the two-phase seepage flow in a composite rock structure with multiscale pores is simulated by this new model, and the effects of viscosity ratio and wettability on the displacement process are discussed. [ABSTRACT FROM AUTHOR]

The problem of seepage control is faced in the construction of large underground powerhouse cavern systems. To reduce leakage and improve the permeability stability of the surrounding rock, a complex seepage control system, including drainage hole arrays, drainage tunnels, and grouting curtains, was designed for the Wunonglong underground powerhouse caverns. In this study, we performed a seepage field numerical analysis of the Wunonglong underground powerhouse caverns system to optimize the seepage control system. A three-dimensional numerical model was established considering the complex seepage control system and the geological conditions. A steady seepage analysis method, with a variational inequality formulation, was adopted in order to calculate the long-term seepage field. A drainage substructure method was used to simulate the seepage behavior of the densely arranged drainage hole arrays. The seepage control effects of single and double grouting curtains were compared to determine a reasonable curtain layout scheme. The effect of the drainage system on the seepage control of the powerhouse caverns is further discussed. The findings offer reliable insights into the seepage behavior of underground powerhouse caverns and provide a reference for the design and construction of similar underground powerhouse cavern systems. [ABSTRACT FROM AUTHOR]

Rigid-wall permeameter testing of two potentially unstable gradations established that the critical hydraulic gradient to trigger instability is smaller for upward flow than for downward flow. The experimental finding is explained with reference to the Skempton-Brogan stress reduction factor α in the finer fraction content of the soil. Theory uses the α-factor to define a hydro-mechanical envelope in gradient-stress space that is independent of flow direction, and the experimental results are found to be in good agreement with the theory. Testing with upward flow is recommended to determine the value of α for an internally unstable gradation because, in contrast to downward flow, there is no requirement for an outflow boundary. [ABSTRACT FROM AUTHOR]

The seepage-stress coupling characteristics of fractured rock mass were studied theoretically in this paper. Based on the cubic law and the equivalent circuit principle, a modified multi-parallel plate equivalent model (MPPEM) for seepage analysis of a rough single-fracture and a modified equivalent seepage resistance model (ESRM) for seepage analysis of a fracture networks consisting of rough single-fracture combined in series and parallel were proposed. On this basis, the equation for the variation of fracture aperture of fractured rock masses under the action of the three-direction principal stresses and pore water pressure was derived, and the discrete element calculations of the seepage-stress coupling of the two-dimensional fractured rock mass were carried out under different ground stress coefficients. The results show that the error of the modified MPPEM characterizing the seepage in a rough single-fracture in a rock mass does not exceed 7%. The modified ESRM can better characterize the seepage in T-shaped combined fracture and × -shaped combined fracture. With the increase of normal stress applied to the fracture surface, the fracture aperture and seepage flow rate of the fractured rock mass decrease. The above study is of great theoretical significance for the analysis of the seepage evolution law of the fractured rock mass under the action of geostress. [ABSTRACT FROM AUTHOR]

A new type of small, dry-filled geotextile tubes is introduced, that, in a stacked formation, can be used as dike cores. Dikes made out of these tubes consist of great potential regarding more resilient flood protection. The geotextile protects the fill from erosion, enabling steeper slopes along with reduced material and less land consumption. The behavior and potential failure mechanisms of such dikes were investigated first by literature research and second by full-scale hydraulic model tests under systematic variation of tube number, number of textile layers, filling ratio, and fill material. The tubes were exposed to the loads of seepage and overflow. Most relevant failure mechanisms were seepage-induced sagging, lateral displacement, and overturning of the upper tube due to overflow. During seepage, the tube height was reduced by up to 22.8 % due to sagging. Overflow led to a lateral displacement of up to 13 cm and, at overflow heights of 23.1 cm and 26.8 cm, to overturning of the upper tube. The present results give new insights into the behavior of innovatively constructed geotextile tubes under hydraulic loads and serve as basis for the development of design rules. • Dry-filled geotextile tubes represent a promising way towards resilient river dikes • Tube behavior is investigated experimentally under parameter variation • Sagging and lateral deformation must be considered in design rules • The tubes withstand overflow heights of >20 cm • Compacting the tubes increases the stability [ABSTRACT FROM AUTHOR]

Permeation grouting – injections at low-pressure values of either microfine cements or chemical products – is frequently adopted to increase the mechanical/hydraulic properties of soils, and standard design approaches are currently either empirical or based on simplified analytical solutions. In this paper, some fundamental hypotheses of these analytical solutions are discussed by carrying out a campaign of finite-element numerical analyses, in which the injection phase in a water-saturated soil is analysed, a Newtonian rheology for the grout is implemented and the hypothesis of immiscibility for the two liquids is assumed. The effect of injection source geometry is discussed, as well as the role of gravity and capillarity. The authors analyse the conditions, in terms of injection flow rate, grout viscosity, soil intrinsic permeability and retention curve, under which the analytical solutions provide reliable results. The numerical results have been compared with the simplified analytical solution herein derived for a one-dimensional spherical geometry, in terms of the 'characteristic curves' for the system: the relationship between injection pressure/grout front advancement and injection time. [ABSTRACT FROM AUTHOR]

High-pressure groundwater brings great challenges to the construction of mountain tunnels. Hence, controlling and discharging groundwater are two key problems that must be addressed before constructing tunnels in high-pressure and water-rich region. Fluid–solid coupling seepage analysis method is used to analyze the variation of displacement, stress and pore water pressure of the tunnel. A waterproof and drainage method suitable for tunnels in high-pressure and water-rich region is proposed. Curtain grouting plays a dual role in waterproof and reinforcing surrounding rock. Decompression drainage holes are designed in order to further reduce the pore water pressure acting on the initial lining. The thickness of grouting circle, the permeability coefficient ratio and the decompression drainage holes distribution rate of the initial lining are the main factors that affect the waterproof and drainage effect of tunnels in high-pressure and water-rich region. Suggested parameters on waterproof and drainage measures for tunnels in high-pressure and water-rich region are given after comprehensive analysis, which can provide basis for the technology on high-pressure groundwater treatments and constructions of underground engineering under complex geological conditions. [ABSTRACT FROM AUTHOR]

Safety conditions in geotechnical structures require the investigation of the phenomena responsible for the loss of their stability. When combined with commonly used direct investigations, geophysical methods add greater efficiency to geotechnical investigations, since their application allows the acquisition of a large amount of data in a short period of time, and at a relatively low cost. In this context, the present study aimed to evaluate percolation through the massif of a small earth dam, based on an integrated interpretation of results obtained with the application of the geophysical methods of Electroresistivity and Self Potential, in addition to results from geotechnical investigations previously carried out on the structure. The results proved the efficiency of the proposed methodology, allowing the confirmation of hypotheses formulated by other authors in previous studies of the same dam. Also, the results allowed the evaluation of the efficiency of correction works carried out in the dam massif to solve the problems caused by a piping process. Among the identified geotechnical properties, a preferential flow path, which indicates the occurrence of a water loss process through the dam foundation layer, was detected and can be linked to the occurrence of a landslide on the downstream slope of the embankment. It can be concluded that the geophysical survey effectively evaluated the geotechnical conditions and seepage within the massif and its foundations, meeting the study's objectives. Both shallow and deep flow paths in the study area were delineated, pinpointing the factors contributing to their occurrence. [ABSTRACT FROM AUTHOR]

This study investigated active and passive lateral earth pressure in the presence of anisotropic seepage conditions. The soil was assumed to be granular and fully saturated. Three methods were used to solve the problem: (1) the upper bound limit analysis method (UBM); (2) upper and lower bound solutions of finite-element limit analysis (FELA); and (3) the stress characteristic method (SCM). The proposed analytical solution for the UBM employed the logarithmic spiral slip surface. The lateral earth pressure coefficients for the active and passive cases were calculated and presented, considering variations in the vertical-to-horizontal hydraulic conductivity ratio, friction angle, and soil–wall interface friction angle. The obtained results for the active and passive cases agree with those of previous studies. The results of the SCM showed that in the presence of seepage, the distribution of stress on the soil–wall interface is nonlinear. In addition, the failure zone obtained from different methods was compared and examined. The failure patterns obtained from the SCM and FELA were almost identical. [ABSTRACT FROM AUTHOR]

To understand the fluid hydraulic behavior change in a fracture under different shear displacements, fluid flow simulations at different flow velocities are carried out based on the Navier–Stokes equation. We characterized and conducted statistics on the change and distribution of the fracture aperture under different shear displacements, especially the measurement of the contact area under shear displacement, which was helpful for accurately studying the effect of shear displacement on fracture fluid flow. The results showed that the shear displacement of a fracture could be regarded as dislocation between the upper and lower fracture surfaces. The fluid flow velocity became larger near the contact sites and the streamlines became denser. The resulting hydraulic aperture exhibited a negative correlation with the contact area. The relationship between the volumetric flow rate and pressure gradient during the flow field simulation could be well-fitted by the Forchheimer equation, and the steepness of the curves was related to the contact area. The linear coefficient a and the nonlinear coefficient b in the Forchheimer equation were positively correlated with the contact area. Based on the measured flow velocity, the mechanical aperture was usually an order of magnitude larger than the hydraulic aperture. The linear relationship between the mechanical aperture and hydraulic aperture was described. The positive correlation between the permeability and mechanical aperture profiled during shear explained the hydraulic behavior in the flow field. [ABSTRACT FROM AUTHOR]

In the last decade, Brazil witnessed disasters relating to tailings dams. This led to changes in the National Dam Safety Policy, which regulates a set of measures to improve dam safety management. In this context, this paper presents a case study of the Ribeirão João Leite dam. The dam consists of a concrete gravity structure with embankment fill at both abutments, placed on a foundation composed of gneiss with quartzite veins. The study aims to investigate its seepage behavior and assess the performance of the seepage control system in the concrete and embankment cross-sections at the right abutment. Two-dimensional seepage analyses under steady-state and transient conditions were performed using the finite element method. A straightforward approach based on monitoring data was proposed to validate seepage analyses and estimate the efficiency of the seepage control system. It was concluded that the foundation of the dam has a significant influence on the pore water pressures and seepage flow behavior due to the presence of markedly fractured materials. The analyses indicated that the efficiency of the grout curtain in the right abutment foundation is not noticeable. On the other hand, the foundation drains play an important role in controlling pore water pressures throughout the dam foundation, even in unfavorable geological conditions. The efficiency of these drains was 28% at the drainage line of Block 2, preventing pressure increases of 36% in the foundation of Block 2 and 160% in the horizontal filter drain. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The post-construction improvement technology of bored pile tips has been widely used in the construction of gravel pebble layers, but the diffusion law of the grouting slurry remains to be revealed. To study the diffusion law of the grouting slurry at the tip of bored piles in gravel pebble layers, an equivalent relationship between the seepage continuity equation and the mass diffusion continuity equation was established based on an in-depth comparative analysis; further relying on the Diluted Species Transport Module in Porous Media of Comsol Multiphysics, a three-dimensional numerical model of slurry diffusion was established to systematically study the impact of key factors such as different porosities, grouting times, grouting pressures, slurry diffusion coefficients, and the ratio of vertical to horizontal slurry diffusion coefficients on the diffusion radius of the slurry. The calculation results show that with the continuation of grouting, the increase in porosity, grouting pressure, and slurry diffusion coefficient, or the decrease in the ratio of vertical to horizontal slurry diffusion coefficients, the diffusion range of the slurry increases accordingly. Furthermore, comparatively speaking, the impact of porosity is the smallest, while the impact of the slurry diffusion coefficient is the greatest. The research findings reflect the diffusion trend of the slurry in the gravel pebble layer, which has guiding significance for the quality control of the actual design and construction of grouting. [ABSTRACT FROM AUTHOR]

Existing methods for calculating the ultimate support pressure of tunnel faces do not consider the control of seepage flow. Therefore, a model for calculating the ultimate support pressure under seepage conditions was established based on a two-dimensional water head distribution model and the upper bound theorem of limit analysis. The reliability of this method was verified through comparisons with other studies. Subsequently, the influence of water level and tunnel face water pressure coefficient on stability was analyzed. The results indicate that the ultimate support pressure is linearly positively correlated with the water level and tunnel face water pressure coefficient; as the water level increases and the water pressure coefficient decreases, the failure area extends and enlarges. Finally, an existing seepage flow calculation formula was introduced, and a method for calculating the ultimate support pressure based on seepage control was proposed. The appropriate tunnel face water pressure coefficient is determined through the seepage flow calculation formula, and the corresponding ultimate support pressure is then calculated. The results demonstrate that this method can provide better theoretical guidance for seepage control in tunnel faces in practical engineering. [ABSTRACT FROM AUTHOR]

In this paper, the research progress made in the methods used for assessing the internal stability of landslide dam soils was reviewed. Influence factors such as the gradation of soil and the stress state in the soil in different analysis methods were discussed, as these can provide a reference for the development of more accurate methods to analyze the internal stability of landslide dam soils. It focuses on the evaluation of internal stability based on the characteristic particle size and fine particle content, hydraulic conditions such as the critical hydraulic gradient and critical seepage velocity, and the stress state such as lateral confinement, isotropic compression, and triaxial compression. The characteristic particle size and fine particle content are parameters commonly used to distinguish the types of seepage failure. The critical hydraulic gradient or seepage failure velocity are necessary for a further assessment of the occurrence of seepage failure. The stress state in the soil is a significant influence factor for the internal stability of natural deposited soils. Although various analysis methods are available, the applicability of each method is limited and an analysis method for complex stress states is lacking. Therefore, the further validation and development of existing methods are necessary for landslide dam soils. [ABSTRACT FROM AUTHOR]

Due to tectonic uplift in the Cenozoic and numerous shelf-wide glaciations during the Quaternary, -1-2.5 km of sedimentary overburden has been eroded from the Barents Sea shelf, leading to the exhumation and partial uncapping of hydrocarbon accumulations. Widespread natural gas and oil leakage from the glacially eroded middle-upper Triassic reservoir directly into the water column has been documented at the Sentralbanken high in the northern Norwegian Barents Sea. However, it remains unclear whether the hydrocarbon leakage occurs only from the middle-upper Triassic reservoir units in geological settings exceptionally conducive to hydrocarbon leakage, or if other reservoir formations contributed to the release of hydrocarbons into the water column. It is also not clear whether complete erosion of the caprock is a prerequisite for widespread liberation of natural gas and oil from glacially eroded reservoirs across Arctic continental shelves. Here we analyze multibeam echosounder data covering -5,000 km2 and a suite of high-resolution P-cable seismic lines from a range of geological structures across the northern Norwegian Barents Sea. Our analyses reveal that -21,700 natural gas seeps originate from exhumed, faulted and variably eroded structural highs bearing a range of Mesozoic reservoir formations. All investigated structural highs fuel seabed methane release hotspots with no exception. Evident from observations of seismic anomalies, fluid accumulations are pervasive in the subsurface and likely to continue fuelling seabed gas seepage into the future. We also document that gas seepage through faults piercing overburden, caprocks and reaching potential reservoir levels is pervasive at all investigated structural highs. On the Storbanken high and the Kong Karl platform, such fault-controlled seepage is more prevalent than seepage from reservoir formations subcropping below the seafloor. Using a simple parametrization approach, we estimate that seeps identified within our multibeam data coverage produce a seabed methane flux of 61 x 107 mol/yr (9,803 ton/yr), which is one to two orders of magnitude higher than other globally known submarine methane seepage provinces. Fluxes of methane from sea water to the air above the thermogenic gas seep provinces in the northern Norwegian Barents Sea remain to be determined. [ABSTRACT FROM AUTHOR]

AbstractThe geological environment of deep coal seam is complex, and the failure mechanism of coal seam under the action of seepage pressure and disturbance stress is unclear, which restricts the development of deep ground engineering. In this study, triaxial compression test of sandstone under seepage-creep-disturbance loading (SCD) was carried out to analyze the characteristics of disturbance deformation, creep rate and permeability. The focus was on the energy evolution law of sandstone under SCD, and the damage creep model was constructed based on the energy proportion. The results show that the creep increment of sandstone under disturbed load was significantly higher than that under undisturbed load, and the stress level can promote the expansion and development of microcracks, in which the creep increment under high stress level showed a jump increase. The total energy and elastic energy of sandstone showed a step change with time. The damage factor under disturbance load was defined in the form of energy dissipation ratio, and the corresponding coupling damage factor was determined by considering the seepage factor and creep factor, which can reflect the coupled damage deformation of sandstone under SCD. Based on fractional order theory, a nonlinear damage creep model describing sandstone deformation under SCD was established by connecting the acceleration element in series with the Nishihara model and introducing the coupling damage factor. This study can provide research ideas for water inrush of coal seam rock mass. [ABSTRACT FROM AUTHOR]

Background: Seepage control measures are essential in earth dams to enhance their safety against seepage and slope failures. A diaphragm is a thin impervious wall that is used in the core area of the dam to prevent the seepage of water. Any crack in the diaphragm can reduce its efficiency and threaten the safety and stability of the dam. Extensive evaluation of the influence of diaphragm fracturing on dam safety is required to establish a safe design and offer the appropriate measures. This study investigates the effect of diaphragm cracking on the safety of the dam for seepage and slope stability. A permeability tank is first used to validate the numerical model; then, different scenarios for cracked diaphragm walls are studied numerically. The crack's height, width, direction, and number are all investigated. The effect of having a downstream horizontal blanket drain with cracked internal diaphragms is also evaluated. Results: The results showed that the internal diaphragm enhances the safety of earth dams as it reduced the seepage discharge by 98% and increased the downstream slope safety by 34%. Considering the development of a crack in the internal diaphragm, the most critical location was at the base of the dam, wider cracks were more destructive, and the most critical direction was the horizontal crack. The fracturing of the diaphragm at multiple locations proved to be detrimental to the safety of the dam. Having three cracks caused the seepage discharge to reach 74% of its value for no diaphragm, the pore water pressure to raise drastically, and the downstream critical factor of safety to be higher than the case of no diaphragm by 8% only. Conclusions: According to the findings, it is advised to continuously monitor the components of diaphragm-type earth dams and perform the necessary maintenance works whenever any sign of damage or water seepage appears. Furthermore, using a well-graded horizontal drain of sufficient length and high permeability with the internal diaphragm is highly recommended as a mitigation measure if diaphragm fracturing occurs. This helps to quickly release the seeping water and keep the phreatic line away from the downstream slope. [ABSTRACT FROM AUTHOR]

This paper describes a simple methodology to calculate the two-dimensional seepage across an infinite unsaturated slope using models of one-dimensional infiltration through horizontal ground. The methodology decomposes the seepage across the infinite slope into antisymmetric and symmetric parts, whose respective solutions are combined to calculate the actual flow regime. The antisymmetric solution is trivial and does not even require integration of the governing continuity equation, while the symmetric solution, albeit non-trivial, reduces to the case of one-dimensional flow through horizontal ground, for which solutions already exist. The methodology is generally applicable to the calculation of distinct seepage regimes across unsaturated slopes with different hydraulic properties under both stationary and transient conditions. The paper also defines the gradient of the piezometric head parallel to the slope, which is the Neumann boundary condition to be imposed on slope sections perpendicular to the ground surface. The rigorous definition of this gradient overcomes the need of imposing arbitrary boundary conditions in finite-element models. Finally, the paper demonstrates that all infiltrated water crosses the slope along the shortest path – namely, the path normal to the surface – while the flow parallel to the slope is entirely fed by an upstream source at infinite distance. [ABSTRACT FROM AUTHOR]

Seawalls are constructed by covering and protecting the sloping seashore ground with concrete plates or blocks. Their purpose is to sustain high waves induced by strong winds and prevent ground erosion, but they often collapse, mobilising different modes of failure, including that of the ground. Nevertheless, limited research has been conducted on ground failure caused by high waves. In this study, a series of novel centrifuge model tests was first conducted to investigate the failure mechanisms of seawalls due to wave propagation, focusing on the failure of the ground. Finite-element analyses were subsequently conducted to explore the failures observed in the model tests and to provide further insight as to the state of the ground leading to failure. Two failure modes were demonstrated to prevail: floating of the covering panel and sliding failure of the ground. In addition, of the possible causes of failure, the following three were identified in the current study: increased unit weight and reduced suction from wetting; enhanced seepage force under the panel and around the toe block during backwash; water pressure on the back of the panel and the landward side of the toe block during backwash. [ABSTRACT FROM AUTHOR]

Grouting has been commonly used for structure controlling in mining engineering. To investigate the mechanism of fracturing grouting, an experiment was conducted under constant flowing conditions. Through the real-time gathering of main parameters and reconstruction of the slurry distribution, the complete grouting process and pressure spread of the high-pressure slurry were revealed. An identification method of fracturing diffusion based on acoustic emission (AE) signals was proposed and verified. The results indicated that the intact rock showed fracturing response with a mutated pressure in a short time. For fractured ones, the grouting process can be divided into five stages: seepage flow, pressure holding, fracturing diffusion, steady flow, and pressure relief. Influenced by the hydraulic fracture and slurry infiltration, there were three states: cement diffusion, water seepage, and the unaffected zone. A calculation method of whole stages for the grouting pressure was proposed based on the Hoek–Brown strength criterion and flow model in a fracture. In addition, AE ring counting occurred during the entire slurry process but was relatively concentrated in pressure holding and fracturing diffusion stages. Considering the zonal distribution characteristics, the AE method was used to characterize the slurry diffusion range and flow paths. The slurry distribution was obtained by the three-dimensional cutting and reconstruction method to verify its feasibility. This study is expected to further clarify the grouting mechanism, and guide engineering practices. Highlights: High-pressure grouting experiment of fractured rock based on acoustic emission was carried out. The whole process of fracturing grouting shows five responses in fractured rock. The pressure calculation model for revealed whole injection process was established in inclined fracture. AE monitoring can be used to identify the splitting-diffusion range and path for fracturing grouting. [ABSTRACT FROM AUTHOR]

Earth-fill dams should be monitored during the first filling of the reservoir to avoid several potential risks. Following the completion of dam construction, the primary safety check is monitoring the dam behavior during the first interaction of the earth material with water. The presented work fills the gap in the literature on the determination of intermediary hold durations of multistage filling schedule and provides insights into the first-filling process. The study investigated the behavior of a 20 m high earth-fill dam model subjected to staged reservoir filling. The durations of the intermediary holds were determined based on coupled stress and pore water pressure analyses using the finite-element method, with a particular emphasis on the transient behavior of the filling process. Hydraulic fracturing and internal erosion possibilities were evaluated based on minimum principal stress and seepage quantities at critical sections. It was observed that the minimum principal stress reaches a local minimum and tends to increase, leading to significant convergence for longer hold alternatives. In addition, seepage quantities exhibited similar behavior of decreasing with longer hold durations. A specific hold duration was recommended for the low-pool level, which resulted in a hold-to-height ratio of 2.35. At the high-pool level, it was found that further waiting has a positive effect in mitigating the risk of hydraulic fracturing and internal erosion initiation. The presented practical methodology is proposed to be used for the design of filling schedules of new dams. Practical Applications: This study provides practical insights for design engineers to determine the first-filling schedule of earth-fill dams. The stress–pore pressure coupled finite-element model information obtained from this study can be helpful for onsite engineers who have access to instrumentation data during the first filling. These data can be used to predict the convergence of key parameters. For intermediary holds at low-pool levels, monitoring minimum principal stress and effective stress behavior over time is crucial to prevent cracking which can lead to hydraulic fracturing if filling continues. Specifically, the initially decreasing principal stress at the upstream face of the core should be closely monitored until an increasing trend is observed, to ensure that sufficient time is allowed before the dam is subjected to higher loads. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High‐resolution modeling of the flow dynamics in fractured soils is highly complex and computationally demanding as it requires precise geometrical description of the fractures in addition to resolving a multiphase free‐flow problem inside the fractures. In this paper, we present an idealized model for saturated–unsaturated flow in fractured soils that preserves the core aspects of fractured flow dynamics using an explicit representation of the fractures. The model is based on Richards' equation in the matrix and hydrostatic equilibrium in the fractures. While the first modeling choice is standard, the latter is motivated by the difference in flow regimes between matrix and fractures, that is, the water velocity inside the fractures is considerably larger than in the soil even under saturated conditions. On matrix/fracture interfaces, the model permits water exchange between matrix and fractures only when the capillary barrier offered by the presence of air inside the fractures is overcome. Thus, depending on the wetting conditions, fractures can either act as impervious barriers or as paths for rapid water flow. Since in numerical simulations each fracture face in the computational grid is a potential seepage face, solving the resulting system of nonlinear equations is a nontrivial task. Here, we propose a general framework based on a discrete‐fracture matrix approach, a finite volume discretization of the equations, and a practical iterative technique to solve the conditional flow at the interfaces. Numerical examples support the mathematical validity and the physical applicability of the model. Core Ideas: Due to the presence of air in dry fractured soils, fractures of large aperture act as capillary barriers.If the capillary barriers are overcome, fractures become fast‐flowing paths for water to travel downward.A flow model based on Richards' equation in the soil and instantaneous ponding in the fractures is proposed.The model is numerically consistent and its physical applicability is showcased in two‐dimensional simulations. [ABSTRACT FROM AUTHOR]

Finding an explicit solution to the widely used Green–Ampt (G–A) one‐dimensional infiltration model has been subject of efforts for more than half a century. We derived an explicit semiempirical approach that combines accuracy with simplicity, a concept that has been generally neglected in previous studies. The equation is F=Kst(0.70635+0.324151+9.43456(S2Ks2t))$F\; = {K_s}\;t\;({0.70635 + 0.32415\sqrt {1 + 9.43456({\frac{{{S^2}}}{{{K_s}^2t}}})} })$, with F (L), Ks (L/T), S (L/T0.5) and t (T) being cumulative infiltration, saturated hydraulic conductivity, sorptivity, and time, respectively. Relative errors (ɛ) by the application of this equation generally do not exceed ±0.3% in most applied infiltration problems faced by water resources engineering today. We show both numerically and mathematically that │ɛ│> 0.3% could only occur if Kst/F > 0.904, a criterion that could apply to sand and loamy sand soils (i.e., coarse texture) and if they experience infiltration rates for over 6 h and 19 h, respectively. Hence, we also derived a simple linear adjustment in the model as Fadj ≅ 0.9796 F + 0.335 S2/Ks to address these longer infiltration rates, and to assure that ɛ remains within the expected ±0.3% range of uncertainty. A linearized regression technique was also developed to accurately estimate S and Ks when the G–A model is used. We numerically demonstrated that our fitting method could be used even when the G–A approach is less valid (diffusive soils), provided that the actual value of the capillary length (λ) is initially known. An added benefit of our approach is that by setting λ equal to 1/3 and 2/3, it can significantly limit the range of initializing, unknown, a priori values of S and Ks, as these two parameters are estimated through the inverse solution of implicit infiltration models. Due to the model's simplicity and accuracy, our solution should find application among hydrologists, natural resource scientists, and engineers who wish to easily derive accurate estimations from the G–A infiltration approach and/or estimate sorptivity and hydraulic conductivity without encountering divergence problems. Core Ideas: A new explicit form of the one‐dimensional Green–Ampt infiltration model was developed.This model combined simplicity, accuracy, and computational efficiency.A new linearized regression solution was derived to estimate sorptivity and hydraulic conductivity.This linearized fitting method can eliminate the risk of convergence associated with other numerical approaches. [ABSTRACT FROM AUTHOR]

Infiltration-runoff-slope instability mechanism of macropore slope under heavy rainfall is unclear. This paper studied its instability mechanism with an improved Green-Ampt (GA) model considering the dual-porosity (i.e., matrix and macropore) and ponding condition, and proposed the infiltration equations, infiltration-runoff coupled model, and safety factor calculation method. Results show that the infiltration processes of macropore slope can be divided into three stages, and the proposed model is rational by a comparative analysis. The wetting front depth of the traditional unsaturated slope is 17.2% larger than that of the macropore slope in the early rainfall stage and 27% smaller than that of the macropore slope in the late rainfall stage. Then, macropores benefit the slope stability in the early rainfall but not in the latter. Macropore flow does not occur initially but becomes pronounced with increasing rainfall duration. The equal depth of the wetting front in the two domains is regarded as the onset criteria of macropore flow. Parameter analysis shows that macropore flow is delayed by increasing proportion of macropore domain (ωf), whereas promoted by increasing ratio of saturated permeability coefficients between the two domains (μ). The increasing trend of ponding depth is sharp at first and then grows slowly. Finally, when rainfall duration is less than 3 h, ωf and μ have no significant effect on the safety factor, whereas it decreases with increasing ωf and increases with increasing μ under longer duration (≥ 3 h). With the increase of ωf, the slope maximum instability time advances by 10.5 h, and with the increase of μ, the slope maximum instability time delays by 3.1 h. [ABSTRACT FROM AUTHOR]

Urugan-type dams are the most common type of dam to work on in Indonesia, with a material composition that is easy to obtain and relatively more economical. Based on the results of slope stability, a sensitivity analysis will be carried out based on changes in slope slope to post-construction conditions, during reservoir operation water level and rapid drawdown conditions. In this study, we will analyze the changes in the value of safety factors that occur on the slope of the body of the Jragung Dam due to rapid drawdown events and seismicities (OBE and MDE) using the help of seepage analysis calculation software and slope stability. There are three models used, namely Model 1 using geometry according to DED (slope of upstream slope 1: 3.0 and slope of downstream slope 1: 2.5), Model 2 of using modification of field construction geometry (slope of upstream slope 1: 2.5 and slope of downstream slope 1: 2.5), Model 3 of using modification of field construction geometry (slope of upstream slope 1: 2.5 and slope of downstream slope 1: 2,25). From the three models, the initial stage will be processed to find the phreatic line on the dam body when drawdown and the next stage to find the value of the dam slope safety factor. After the overall analysis was carried out both in terms of seepage analysis and stability analysis of the three simulation models, for the construction in the field on the Jragung dam, the 3rd Model can be used, namely the proposed geometric modification with an upstream slope of 1: 2.5 and a downstream slope of 1: 2.25, and material parameters according to the availability specifications at the work site. Regarding the stability of the slope, it is noted that at the time of the MDE earthquake load of 10,000 years, when the rapid-drawdown conditions y/h = 0.5h and y/h = 0.75h there is a possibility that the Jragung dam will be damaged, but not collapsed. [ABSTRACT FROM AUTHOR]

The study of rough fissure seepage and grouting diffusion, slurry consolidation and filling, as well as the seepage reduction law is of great significance for the detection of grouting effect and water damage prevention and control in fissured rock bodies. To this end, a new technology combining three-dimensional scanning and 3D printing was used to batch prepare a visualization test model based on the morphology of real rock fissures, and carry out visualization tests of seepage in rough single fissure, grouting with different water-cement ratios, and seepage after grouting and consolidation filling of fissures. The test results show that: Rough single fissure seepage in the seepage path and seepage law are non-linear characteristics, for the laminar and turbulent flow of the composite flow form; in the equal flow conditions, the water-cement ratio of small slurry has a pre-diffusion of slow in the middle and late fast, the total time instead of the characteristics of the less; slurries with different water-cement ratios fill and consolidate extremely unevenly in the cracks, and the cross-sectional void ratio gradually decreases from the entrance to the end, while the overall filling rate can be increased by up to 20% in slurries with small water-cement ratios; the seepage coefficient of the fissure before and after slurry filling decreased by a factor of 100–1000, and the seepage flow was along the connected gap network and conformed to the nonlinear characteristics of Forchheimer's equation, and with the decrease of water-cement ratio, the coefficients of the nonlinear term and the coefficients of the linear term increased and decreased, respectively, and the ratio of both of them could reach a maximum value of 102. [ABSTRACT FROM AUTHOR]

Using one opening (filter) within the floors of hydraulic structures is a known technique to relieve the seepage effects on their floors. In this study, a new method to control seepage flow by using two identical filters instead of one was tackled numerically. A comparative analysis of using one versus two filters was conducted for different thicknesses of the permeable stratum, apron size (b), filter length, and sheet pile wall depths. Results indicate that two filters are considerably more effective than using one where the overall uplift force, the maximum potential head, and the hydraulic exit gradient downstream of the floor are reduced to 42–56%, 42–51%, and 66–76%, respectively, compared to one filter, while slightly increasing seepage flow by 1–7%. Many reasons can lead to horizontal openings (cracks) appearing along the sheet pile walls beneath hydraulic structures. The current study tackled their effects on seepage flow for the first time and examined their impact on the floor. A crack in the upstream sheet pile wall can increase total uplift forces by up to 40%, while a crack in the downstream sheet pile wall can increase the hydraulic exit gradient by up to 230% [ABSTRACT FROM AUTHOR]

The permeability coefficient of landslide mass, a key parameter in the study of reservoir landslides, is commonly obtained through in situ and laboratory tests; however, the tests are costly and subject to high variability, leading to potential biases. In this paper, a new method was proposed to inversely estimate the permeability coefficient of landslide layers using monitoring data of groundwater level (GWL). First, the landslide transient seepage simulation was conducted to generate sample data for permeability coefficients and GWL during a reservoir operation cycle. Second, using GWL data as input and permeability coefficient data as output, the least-square support vector machine (LSSVM) was trained with two optimization algorithms, the particle swarm optimization (PSO) algorithm and the whale optimization algorithm (WOA), to construct the nonlinear mapping relationship between simulated GWL and permeability coefficients. Third, the accurate permeability coefficients for landslide seepage simulation were inverted or predicted based on the monitored GWL. Finally, using the inverted permeability coefficients for landslide seepage simulation, we compared simulation results with actual monitored GWL and achieved good consistency. In addition, this paper compared the inversion effects of three different algorithms: the standard LSSVM, PSO-LSSVM, and WOA-LSSVM. This study showed that these three algorithms had good nonlinear fitting effects in studying landslide seepage fields. Among them, using the inversion values from PSO-LSSVM for landslide seepage simulation resulted in the smallest relative error compared to actual monitoring data. Within a single reservoir operation cycle, the simulated water level changes were also largely consistent with the monitored water level changes. The results could provide a reference to determine landslide permeability coefficients and seepage. [ABSTRACT FROM AUTHOR]

Fluctuations in reservoir water levels have a significant impact on the seepage and slope stability of earth dams. The varying rate of the water level and soil–water characteristic curve (SWCC) hysteresis are the main factors affecting the seepage and the stability of dam slopes; however, they are not adequately considered in engineering practices. In this study, the SEEP/W module and the SLOPE/W module of Geo-studio were employed to analyze the seepage features and the stability of downstream slopes, taking into account the water level fluctuation rate and the SWCC hysteresis. The results reveal that the pore water pressure of the representative point forms a hysteresis loop when the water level fluctuates, which becomes smaller as the water level variation rate increases. Within the loop, the pore water pressure with a rising water level is greater than the value when the water level is dropping, and the desorption SWCC derives greater pore water pressures than the adsorption SWCC. Similarly, the safety factor (Fs) curves under the condition of water level fluctuations also form a hysteresis loop, which becomes smaller as the variation rate of the water level increases. When the water level fluctuation rate increases to 4 m/d, the two curves are tangent, meaning that the Fs with a rising water level is always greater than the value when the water level is dropping. The desorption SWCC derives a lower Fs value than the adsorption SWCC as the water level draws up, but this initiates no evident difference in the Fs value when the water level draws down. These findings can be used to inform the design and operation of earth dams under fluctuating water levels. [ABSTRACT FROM AUTHOR]

The rough structure in natural fractures will have impact on the fluid flow performance. It is difficult to understand its mechanism through direct research because of complex and disordered structure. In this context, a digital roughness crack model and introducing artificial roughness elements are constructed. And a crack simulation program based on the Lattice Boltzmann Method was written and verified to study the mechanism of the effect of crack roughness on seepage. The results show that: (1) Artificial elements with different shapes have different effects on fluid flow in the fracture, which are reflected in the local flow pattern. The rectangular element has the greatest obstruction effect on the fluid, and has the most developed vortex structure locally. The semicircular element and the triangular element have a decreasing effect on the fluid flow, and the degree of development of the local vortex is also reduced. (2) It is found that the interaction effect between height and distance disappears when the height is the same and the ratio of the distance and height between adjacent roughness elements is greater than 5 and two opposite vortices between adjacent rough elements merge into one. (3) The existence of roughness elements in rough fractures will have a strong viscous effect on the fluid. And with the change of the shape of the roughness element, the resistance strength of the viscous effect to the fluid is also different. The research results help to understand the seepage law of fluid flowing in rough fractures, and have certain reference significance for industrial applications such as oil production. [ABSTRACT FROM AUTHOR]

The rheological properties and seepage laws of fractured rock masses have a highly significant impact on the long-term stability of engineering rock masses. To study the rheological properties and seepage laws, rheological experiments under different loading paths were designed and conducted on sandstone samples with pre-fabricated single fractures. The results indicated that (1) as the axial stress or pore pressure increases, or the confining pressure decreases, the creep strain (both axial and radial directions) during the creep tests increases, and their stain rate decreases; (2) compared to the pore pressure, the axial stress and confining pressure have a more significant influence on the flow rate during the creep process. As the axial stress increases or the confining pressure decreases, the flow rate shows an increasing trend; (3) the higher connectivity results in higher final flow in an exponential function, indicating that the connectivity ratios can well reflect the permeability of the fractures; (4) the changes in the stress field may lead to the transition of the surrounding rock from a stable state to an unstable state, i.e., the occurrence of creep failure, or water inrush. Therefore, when the state of the surrounding rock changes, strengthened monitoring and proper preventive measures should be implemented.

Abstract Background Seepage control measures are essential in earth dams to enhance their safety against seepage and slope failures. A diaphragm is a thin impervious wall that is used in the core area of the dam to prevent the seepage of water. Any crack in the diaphragm can reduce its efficiency and threaten the safety and stability of the dam. Extensive evaluation of the influence of diaphragm fracturing on dam safety is required to establish a safe design and offer the appropriate measures. This study investigates the effect of diaphragm cracking on the safety of the dam for seepage and slope stability. A permeability tank is first used to validate the numerical model; then, different scenarios for cracked diaphragm walls are studied numerically. The crack’s height, width, direction, and number are all investigated. The effect of having a downstream horizontal blanket drain with cracked internal diaphragms is also evaluated. Results The results showed that the internal diaphragm enhances the safety of earth dams as it reduced the seepage discharge by 98% and increased the downstream slope safety by 34%. Considering the development of a crack in the internal diaphragm, the most critical location was at the base of the dam, wider cracks were more destructive, and the most critical direction was the horizontal crack. The fracturing of the diaphragm at multiple locations proved to be detrimental to the safety of the dam. Having three cracks caused the seepage discharge to reach 74% of its value for no diaphragm, the pore water pressure to raise drastically, and the downstream critical factor of safety to be higher than the case of no diaphragm by 8% only. Conclusions According to the findings, it is advised to continuously monitor the components of diaphragm-type earth dams and perform the necessary maintenance works whenever any sign of damage or water seepage appears. Furthermore, using a well-graded horizontal drain of sufficient length and high permeability with the internal diaphragm is highly recommended as a mitigation measure if diaphragm fracturing occurs. This helps to quickly release the seeping water and keep the phreatic line away from the downstream slope. Graphical abstract

The water repellency of soil occurs when organic matter coats the soil particle surface; this can either happen naturally due to wildfire and fungal growth or be induced by chemical treatments. The internal stability of water-repellent soils subjected to seepage has not been explored in the literature. In this study, the mechanical responses to internal erosion in three synthetic water-repellent soils, treated by different organic matters, were first investigated using a modified stress-controlled triaxial apparatus. The degree of hydrophobicity of the test soils was assessed through the measurement of apparent water contact angle. In each internal erosion test, the cumulative particle loss, deformation and hydraulic conductivity were evaluated. The water-repellent coatings efficiently suppressed the progression of internal erosion at practical hydraulic gradients because of their smaller fluid–solid adhesion. Continuously increasing the hydraulic gradient would finally result in a breakthrough of internal erosion due to the saturation of the hydrophobic soils under high pore-water pressures. Post-erosion contact angle measurements and scanning electron microscopy images confirmed the durability of the three water-repellent coatings against seepage erosion. The findings of this study confirm the potential of applying hydrophobic soils to mitigate internal erosion under normal hydraulic loading conditions. [ABSTRACT FROM AUTHOR]

Accurately assessing the erodibility of geomaterials is of great significance for the design of earthen structures and the prevention of the associated failure induced by seepage force. Recently, the un-resolved Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) has been widely used to investigate internal erosion. However, due to the use of wall boundary and the fact that the fixed CFD domain cannot be changed with the soil sample's volume contraction during the erosion test, a larger porosity at the boundary of the CFD domain is commonly formed, resulting in sidewall preferential flow (i.e., relatively more fine particles migrate along the boundary of the DEM domain) and thereby overestimating the soil erodibility. In this study, a new method based on particle boundary is developed to tackle this problem. The newly proposed particle boundary can prevent its particles from erosion via inter-particle bonding and transfer stress from servo walls to the simulated sample. An optimal particle boundary thickness is determined by considering sample contraction and computational efficiency. The performance of the new method was compared with the conventional method and also verified using experimental results. The results show that the newly proposed method has significantly improved the uniformity of fluid velocity distribution. Furthermore, the cumulative eroded mass of fine particles in the new model is approximately 15% lower than in the conventional model. It is convincingly demonstrated that the new method can simulate internal erosion better and give a more accurate assessment of geomaterial erodibility. [ABSTRACT FROM AUTHOR]

In order to truly describe the dynamic characteristics of bottom-hole pressure in the reservoir, in this paper, the elastic outer boundary condition is introduced to replace the three kinds of traditional outer boundary conditions (infinity, constant pressure, closed), and a spherical nonlinear seepage model is established for the dual-porosity reservoir, which takes into account wellbore storage, effective well diameter and quadratic gradient term. The solution of the model in the Laplace space is found, and the similar structural formula of the solution is obtained by combining the Laplace transformation with the similarity construction method. Subsequently, by the Stehfest numerical inversion method, the well test curve is drawn, and the influence of main reservoir parameters on bottom-hole pressure dynamics is analyzed. The introduction of the elastic outer boundary not only breaks the traditional fixed form of the ideal outer boundary condition, but also improves the interpretation accuracy of the reservoir boundary. At the same time, a more general representation of the model is put forward, which provides a more effective theoretical basis for further exploration of the seepage law of the reservoir. Simultaneously, the similarity construction method simplifies the complex calculation process of solving the model and provides a new idea for solving the more complicated percolation model of oil and gas reservoirs. The similar construction method simplifies the complicated calculation process of solving the model and provides a new idea for solving the more complicated percolation model of oil and gas reservoirs. [ABSTRACT FROM AUTHOR]